1. Field of the Invention
The present invention is directed to an apparatus for generating acoustic waves of the type having a liquid lens for focusing the acoustic waves.
2. Description of the Prior Art
Generators for generating acoustic waves are known which include a source of acoustic waves with which the acoustic waves can be introduced into an acoustic propagation medium, and a variable focal length liquid lens arranged in the acoustic propagation medium. The liquid lens has two lens walls and a lens liquid situated therebetween and it is known to employ means for deforming at least one of the lens walls for the purpose of varying the focal length.
Such generators, for example can be designed as pressure pulse generators for medical purposes, for example for treating stone pathologies (lithotripsy), tumors or bone conditions (osteorestoration). Such generators, moreover, can be designed as pressure pulse generators utilized in testing materials, with which specimens of material are charged with pressure pulses. Further, such generators can be designed as medical ultrasound generators for diagnostic purposes (for example, ultrasound imaging) or therapeutic purposes (for example, hyperthermia) as well as other types ultrasound generators that serve the purpose, for example, of testing materials or other purposes. In all cases, the acoustic propagation medium serves the purpose of conducting the generated acoustic waves from the source of acoustic waves in the direction of the subject to be acoustically irradiated. The generator and the subject to be acoustically irradiated must be aligned relative to one another such that the specific region of the subject to be acoustically irradiated is situated in the focal region of the acoustic waves, i.e. in the focal region of the liquid lens. The focal length of the liquid lens can be varied in order to be able to match the distance of the focal region of the acoustic waves from the surface of the subject to be acoustically irradiated to the respective requirements. German Published Application 37 39 393 discloses a generator fashioned as a medical pressure pulse generator, namely as a lithotriptor. In the case of the known generator, the means for deforming at least one lens wall are fashioned as a mechanical adjustment device that has a complicated structure and tends to malfunction under certain circumstances. A solution disclosed by German Utility Model 85 23 024, corresponding to U.S. Pat. No. 4,718,421 improves upon this, by providing means for deformation that are actuated by pressurized agents instead of using mechanical adjustment. It is often desirable, however, to employ a locating system in combination with the acoustic wave source, in which case an opening preferably a central opening, must be provided for the component, such as an ultrasound scanner, which generates the locating field. Since the deformable lens wall in the aforementioned known system is executed as a flexible membrane, it is not possible without further complications to provide a central opening for the acceptance of the ultrasound head of an ultrasound locating systems.